The letter originated in Irish writing[2] as a d with a cross-stroke added. The lowercase version has retained the curved shape of a medieval scribe's d, which d itself in general has not.

In Icelandic, ð represents a (usually apical) voiced alveolar non-sibilant fricative[ð̠],[3][4] similar to the th in English "the", but it never appears as the first letter of a word, where þ is used in its place. The name of the letter is pronounced [ɛθ̠]; i.e., voiceless, unless followed by a vowel.

In Faroese, ð is not assigned to any particular phoneme and appears mostly for etymological reasons; however, it does show where most of the Faroese glides are, and when the ð is before r it is, in a few words, pronounced [ɡ]. In the Icelandic and Faroese alphabets, ð follows d.

In Old English, ð (referred to as ðæt by the Anglo-Saxons[citation needed]) was used interchangeably with þ (thorn) to represent either voiced or voiceless dental fricatives. The letter ð was used throughout the Anglo-Saxon era, but gradually fell out of use in Middle English, practically disappearing altogether by 1300;[5]þ survived longer, ultimately being replaced by the modern digraph th.

The ð is also used by some in written Welsh to represent the letter 'dd' (the voiced dental fricative).[6]